Rock Bolt

ABSTRACT

A rock bolt is for use in stabilizing a rock face. The rock bolt comprises a body having a plurality of elongate lobes spaced apart by substantially resilient channel means. The rock bolt is further configured to receive expansion means for urging the lobes outwardly to thereby expand the rock bolt for improving a communication with a bore hole in the rock face. Following expansion the expansion means may be removable, the expansion means can comprise any suitably sized hollow or solid bar expansion member. The configuration of the present invention also enables, subsequent to an initial expansion, the resilient channel means to provide a gripping force on any suitably sized member inserted into the internal space. This feature of the rock bolt allows for a mesh plate having an elongate portion to be securely and removably fitted to the rock bolt after the rock bolt has been expanded.

TECHNICAL FIELD

The present in relate to a rock bolt.

BACKGROUND

It is known to use rock bolts for improving the structural integrity of a rock body to increase the environmental safety of a mining operation. Typically rock bolts are fitted into a bore hole in a rock face of a rock body such as in an underground mine roof or wall for example. The rock bolt is fitted in order to support the rock face in the event of a sudden rock body fault or creep movement and thereby prevent or limit a collapse of the rock face.

In applications where the rock body permits a generally constant bore hole diameter it is known to use rock bolts that are designed to yield and fail progressively under a load in order to avoid a sudden and catastrophic failure of the rock bolt in the event of a rock face movement.

In other rock body conditions where variations in a bore hole diameter are more common it is known to use generally tubular rock bolts having an outer diameter arranged to accommodate changes in the bore hole diameter and still be able to safely support the rock face. Known means for allowing a variable outer diameter of a rock bolt include rock bolts having a longitudinal split that can be closed to accommodate a bore hole diameter that decreases in size after the rock bolt is installed. Similarly, it is known to use a rock bolt having a single longitudinal channel running along the surface of the rock bolt, the channel is partially compressed for allowing both a degree of compression to accommodate a bore hole that decreases in diameter, and alternatively, a degree of expansion to accommodate a bore hole that increases in diameter.

In such rock bolts the degree of compression and/or expansion is limited. It is known to use high pressure hydraulic systems to expand an installed rock bolt however such methods are time consuming and costly to operate and in use it is difficult to alter the expansion to suit the environmental conditions of the bore hole and/or rock body into which the rock bolt is fitted.

Problems arise with prior art rock bolts which have a single longitudinal channel as they lack symmetry when the rock bolt is installed into the bore hole. During installation the rock bolt is compressed and this has the effect of changing a cross sectional profile of the rock bolt from a generally circular configuration to a generally elliptical configuration. The result is that a circular bore hole is fitted with an elliptical rock bolt having a cross sectional profile with a major axis and a minor axis. A contact between the bore hole and the rock bolt being substantially limited to the two peripheral ends of the major axis. Accordingly the effectiveness of such rock bolts to engage the bore hole is compromised.

Further, it is known for rock bolt having a single longitudinal channel or a longitudinal split to twist about a longitudinal axis of the rock bolt during installation into a bore hole. Twisting of prior art rock bolts alters the rock bolt cross sectional profile and it is found that such twisting can lead to an irregular and unpredictable cross sectional profile along the length of the rock bolt. Accordingly the effectiveness of such rock bolts to engage the bore hole is compromised.

The present invention attempts to overcome at least in part the aforementioned limitations of previous rock bolts.

It is an object of the present invention to provide a rock bolt which does not twist and in use retains as substantially symmetrical and generally circular profile.

It is an object of the present invention to provide a rock bolt comprising expansion means for selectively varying a radial expansion of the rock bolt in situ in a bore hole of a rock face.

It is an object of the present invention to provide a rock bolt which provides at least three spaced apart points of contact between the rock boll and the bore hole at any point along a working length of the rock bolt.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention there is provided a rock bolt comprising a body having a first end and a second end with a length along a longitudinal axis, the body comprising a wall having an internal surface defining an internal space, the wall comprising a plurality of elongate lobes, for engaging a bore hole surface each lobe having a radial and longitudinal dimension, adjacent lobes being spaced apart and connected together by channel means running, at least in part, along the length of the rock bolt, wherein the channel means comprises wall sections connected together and configured to provide a substantially resilient inwardly disposed junction between adjacent lobes.

In accordance with a farther aspect of the present invention there is provided expansion means comprising a body having a first end and a second end defining a length along a longitudinal axis, the expansion means arranged to be forcefully inserted into the internal space of the rock bolt in situ in a bore hole, wherein the expansion means engages the internal surface of the rock bolt thereby urging the rock bolt to expand outwardly for improving the engagement with a bore hole surface.

Preferably the plurality of elongate lobes are radially spaced about the longitudinal axis, and preferably there are three lobes.

Preferably the rock bolt comprises connection means for assisting in operation and handbag of the rock bolt. Preferably the connection means comprises a collar disposed proximal the second end.

In a preferred embodiment the rock bolt comprises a portion substantially free of channel means. Preferably the portion is disposed between the connection means and the second end.

Preferably each lobe comprises a contact surface for abutting a bore hole surface, preferably a curvature of the contact surface is configured to be variable and before fitting to a bore hole, each contact surface comprises a portion having a greater curvature than the bore hole surface.

Preferably the expansion means engages with one or more inwardly disposed junctions for urging the lobes into a radial expansion to improve a contact between the rock bolt and the bore hole surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a partial perspective view of a rock bolt in accordance with a preferred embodiment of the present invention;

FIG. 2 is a partial side view of the rock bolt of FIG. 1;

FIG. 3 is an end view of a first end of the rock bolt of FIG. 1;

FIG. 4 is a simplified cross sectional of view along a-a of the rock bolt of FIG. 1;

FIG. 5 is a perspective view of a connection means of the rock bolt of FIG. 1;

FIG. 6 is a view in cross section of the connection means of FIG. 5;

FIG. 7 is a schematic cross sectional view showing the rock bolt of FIG. 1 partially fitted with an expansion member and undergoing an outward expansion

FIG. 8 is a perspective view of the rock bolt of FIG. 1 receiving an expansion member; and

FIG. 9 is a partial perspective view eta second end oldie rock bolt of FIG. 1.

DESCRIPTION OF THE EMBODIMENTS

Referring to FIGS. 1 and 2 there is shown a rock bolt 10 in accordance with a preferred embodiment of the present invention. The rock bolt 10 comprises an elongate body 12 having a first end 14 and a second end 16 defining a length along a longitudinal axis. The body 12 is arranged to be substantially hollow having a lumen or internal space 18 extending substantially along the length of the body 12. The body 12 comprises a wall 15 having an outer surface 20 and an inner surface 21. The wall 15 being configured to provide a plurality of elongate lobes 22, each lobe 22 having a radial profile (see FIGS. 3 and 4 extending longitudinally along the body 12. Adjacent lobes 22 being spaced apart and connected together by channel means running along, at least in part, the length of the rock bolt 10.

As seen in FIG. 3 and FIG. 4 (shown in cross section only), each lobe 22 comprises a contact surface 41 which in use abuts with a surface oldie bore hole. The contact surface 41 is configured to be arcuate and complementary at least in part with the bore hole suffice.

It has been advantageously found that baying the lobes 22 configured with a greater curvature than the bore hole allows the lobe 22 to be variable by being compressed and flattened out upon installation or expansion of the rock bolt 10 for assisting in achieving an improved communication and engagement between the contact surface 41 and the bore hole surface.

Further, when the rock bolt 10 is compressed to fit into a bore hole the unique configuration of the rock bolt 10 combined with a resilient property of the metallic construction material provides an internal tension in the rock bolt 10 that biases the lobes 22 to remain in contact with the bore hole surface. Preferably the rock bolt 10 is made from a mild steel. In light of the resilient features of the rock bolt 10, it is envisaged a higher grade steel having a relatively high tensile strength will give best results. Given the known corrosive environment of a mine a material having good corrosion resistance is also be preferred.

As can be seen in the Figures, the body 12 comprises a generally tubular configuration and preferably a generally cylindrical tubular configuration. As shown in FIGS. 1 and 2, the body 12 first end 14 is arranged to be tapered such that at least a portion of first end 14 has a lesser cross sectional area than a cross sectional area of the second end 16, as seen in FIG. 3. Preferably the first end 14 and the second end 16 are arranged to be open.

As seen in FIG. 4, in a preferred embodiment of the present invention the channel means comprises a plurality of longitudinal and inwardly disposed channels 24. The channel means comprises three channels 24 with each channel 24 spaced evenly about the outer surface 20. As shown in FIG. 4, each channel 24 comprises adjacent wall sections 26 having a first outer end 25 and a second inner end 27, the outer end 25 connecting with an adjacent lobe 22. Adjacent wall section 26 inner ends 27 join together to provide a junction 28. In a preferred embodiment of the present invention as seen in FIGS. 3 and 4 the channels 24 and thus the lobes 22 are generally radially spaced around the longitudinal axis by about 120°. It is advantageously found that this configuration also improves a torsional stiffness of the rock bolt 10 which in use limits a twisting of the rock bolt 10 during or after installation.

Accordingly, in a preferred embodiment as shown in the FIG. 4 the rock bolt 10 comprises three independent contact suffices 41. It is to be understood that the channel means general dimensions, such as the number of channels 24 or the shape or configuration of each junction 28, may be altered to vary a strength characteristic of the rock bolt 20. Preferably the channels 24 are integral with the body 12 and are formed during an initial roll forming operation to manufacture the body 12, or in a secondary cold drawing fabrication process upon an initially substantially tubular body 12.

In a preferred embodiment of the present invention the rock bolt 10 second end 16 comprises a connection means. As seen in FIGS. 5 and 6 the connection means comprises a collar 30. The collar 30 being arranged proximal the rock bolt 10 second end 16 and held in position by, for example, swaging and/or welding. A working length of the rock bolt 10 being disposed between the first end 14 and the collar 30.

As shown in FIGS. 5 an 6, the collar 30 comprises a body 32 having an inner end 34 and an outer end 36 defining a collar length along a longitudinal axis. The collar 30 comprises an outer surface 38 which is preferably contoured to include a curved, beveled and/or tapered portion 40 proximal the inner end 34 and also include a recessed portion 42 between the inner end 34 and the outer end 36. The collar 30 is preferably hollow comprising a lumen 44 extending between the inner end 34 and the outer end 36. It is to be understood the lumen 44 is dimensioned to receive the rock bolt 10 second end 16.

In a preferred embodiment of the present invention shown in FIG. 2 and FIG. 9 the rock bolt 10 comprises a portion 11 having no channel means proximal to the collar outer end 36. The portion 11 is arranged to be substantially free from any channel means so as to provide as full circumferential join between the collar 30 and the rock bolt 10. It has been advantageously found that having a full circumferential join, preferably a weld, between the collar 30 and portion 11 increases a pull load rating of the collar 30 and is more effective than prior art rock bolts which have a collar that does not have a full circumferential join and is therefore weakened by a break in the join.

In alternate embodiments (not shown) of the present invention the connection means may be integral with the rock bolt 10 second end 16. In such embodiments it is to be understood that the recessed portion 42 and tapered portion 40 would be integral with the rock bolt 10 outer surface 20.

In further alternate embodiments the connection means may have provision of a first annular portion or pull ring (not shown) about the collar 30. In use, such a pull ring is utilised for conducting a pull test upon an installed rock bolt 10 to determine a load that the rock bolt 10 may carry. Preferably the connection means comprises a second annular portion or retaining ring (not shown) utilised for retaining for example a mesh bearing plate (not shown) to support wire meshing against the rock face as is known in the art.

Preferably the pull ring has a larger outer diameter than the retaining ring and is disposed between the retaining ring and the connection means outer end 36 so that in the event that a mesh bearing plate detaches from the retaining ring it will then be substantially engaged by the pull ring and thus remain supported by the rock bolt 10.

Preferably a method of fabrication is employed during manufacture of the rock bolt 10 for simultaneously forming the taper at the first end 14 and the portion 11 at the second end 16. The method of fabrication comprising a taper block having a tapered opening for receiving and shaping the first end 14, one or more holding blocks spaced along the length of the rock bolt 10 for stabilising the rock bolt 10, and a hydraulic cylinder having a tapered mandrel adapted to be received within the second end 16.

Preferably the tapered mandrel also comprises a cylindrical wall defining a sleeve dimensioned to support the outer surface 20. In use the mandrel engages the second end 16 and urges the channel means outwardly until the second end 16 undergoes a plastic deformation as the channel means, at least along portion 11, are compressed and the second end 16 takes on a substantially circular and tubular configuration without channel means.

As seen in FIGS. 7 and 8, in a preferred embodiment of the present invention the rock bolt 10 further comprises an expansion means. Preferably the expansion means comprises an insertion member 70. The insertion member 70 having a first end 72 and at second end 74 defining a length therebetween. The insertion member 70 comprises a substantially resilient body 75 having an outer surface 76. Preferably the body 75 has a circular configuration, such as for example a tubular cylinder, or rod.

It is to be understood that the insertion member 70 is arranged to be inserted into the internal space 18 of rock bolt 10 and therefore has a lesser outer diameter ‘D’ than an inner diameter ‘d’ of the rock bolt 10. It should also be appreciated that the insertion member 70 is adapted to engage with the inner surface 21 of the rock bolt 10 wall 15.

Preferably the insertion member 70 engages with the plurality of inwardly disposed junctions 28 thereby urging the lobes 22 to undergo an outward displacement. The lobe 22 contact surface 41 and/or channel means may undergo a deformation which has a plastic and an elastic component as a scope of outward displacement is maximised.

The insertion member 70 may have a collar fixed to the second end 74 configured to support a mesh bearing plate (not shown) for holding mesh as is known in the art.

Preferably the insertion member 70 first end 72 may be tapered to assist an operator locating the insertion member 70 within the rock bolt 10 during installation of the insertion member 70. It is to be understood the portion 11 having no channel means also assists the operator to locate the insertion member 70 with the second end 16 during installation.

It is to be understood that installation of an insertion member 70 to a fitted rock bolt 10 results in an improved and a tighter communication between lobe 22 contact surface 41 and the bore hole surface thereby increasing the efficiency of the rock bolt 10 to grip the bore hole surface for preventing or limiting a collapse or movement of the rock face.

As seen in FIG. 7 the insertion member 70 may comprise a collar 30 such as that seen in FIGS. 5 and 6. In a preferred embodiment of the present invention the collar 30 may be fixed to the insertion member 70 by known means such as welding, crimping or a simple complementary threaded arrangement in which case the collar 30 may be removable. The collar 30 may also provide a contoured surface, such as for example a threaded portion (not shown) or a recessed portion 42, arranged for engaging other equipment or apparatus such as, for example, a jumbo rig (not shown) for a forceful installation of the expansion member 70 into a rock bolt 10 or for supporting a mesh bearing plate (not shown) for holding a mesh against the rock face as is known in the art.

In use the insertion member 70 may be forcefully inserted into the internal space 18 of a rock bolt 10 in situ in a rock face bore hole. It is to be understood that the insertion member 70 is dimensioned such that the outer surface 76 engages with at least an internal surface 21 (see FIG. 3) of a junction 28. As the insertion member 70 penetrates into the internal space 18 it provides an outwardly deforming force upon the plurality of junctions 28 thereby urging the rock bolt 10 into a radial expansion and forcing the lobes 22 outwardly as shown schematically in FIG. 8.

It is to be understood that fitting of an insertion member 70 to a rock bolt 10 has the effect of urging the lobes 22 to expand outwardly as shown in FIG. 8 and consequently bring the rock bolt 10 into a tighter communication with the bore hole. It is also to be understood that the resilient nature of the rock bolt 10 provides a feature which can act to grip and hold the insertion member 70 in place within the internal space 18. As such the present invention provides a rock bolt 10 within which an insertion member 70 may be held in place by the plurality of junctions 28. It should be understood that the insertion member 70 can act to retain meshing while being held in place by the rock bolt 10. Accordingly a pull test may be carried out on an insertion member 70 alone, whereby if it fails another expansion member 70 having a slightly greater outer diameter ‘d’ may be fitted, for example, to increase the grip and hold of the insertion member 70 to improve the pull test results.

It should be understood the expansion means of the present invention may comprise any member capable of being inserted into the internal space 18 and/or engaging with the inner surface 21. One typical expansion means may comprise a wedge piece which may be inserted into the internal space 18 upon installation and then removed after the rock bolt 10 has been expanded.

As mentioned above, once inserted the expansion means is subject to a substantially equal and opposite force to thereby hold the expansion means in place within the internal space 18. It should be understood this feature of the present invention may be utilized by fitting a collar 30 or plate to an insertion member 70 and in effect using the rock bolt 10 as a socket in which the insertion member 70 may be reversibly held.

Alternatively after expanding a rock bolt 10 the expansion means, such as a wedge piece, may be removed from the internal space 18. In such cases it is to be understood the plastic deformation of the channel means and the lobe 22 ensure the rock bolt 10 has a lighter fit with the bore hole than prior to insertion of the expansion means.

A mesh plate having an elongate portion (not shown) may subsequently be fitted to an expanded rock bolt 10 for holding mesh as is known. It should be understood the elongate portion is forcefully inserted into the internal space 18 engaging with and elastically deforming the resilient junctions 28 which then provide a gripping force to bold the mesh plate in position. The elongate portion may have a solid or hollow configuration. Preferably the elongate portion is also around 880 mm in length, and may be subject to some deformation during and after installation into the internal space 18.

In use, a rock bolt 10 in accordance with the present invention is installed into a bore hole (not shown) in a rock face (not shown) by known means such that the rock bolt 10 first end 14 and a working length of the body 12 are substantially contained within the bore hole and the collar means is substantially external to the bore hole and typically level with the rock face. It is to be understood that a bore hole's dimensions will be complementary to the rock bolt 10 and vice versa. Typically a bore hole will have a slightly smaller cross sectional area approximately 42-22 mm than the rock bolt 10 approximately 46-48 mm so that the rock bolt 10 is compressed during and after installation. However, other embodiments may include a rock bolt 10 fitted to a larger bore hole and expanded therein by using an insertion member 10.

In one embodiment of the present invention the rock bolt 10 comprises a threaded portion (not shown) projecting from a first end 14 thereof. In use such a threaded portion may be used to point anchor the rock bolt 10 with the use of a complementary mechanical wedge member (not shown) as is known in the art

If required, an operator may apply a grout to the internal space 18 of an installed rock bolt 10. Typically grout is applied via the open second end 16 and urged into the internal space 18. Air within the internal space 18 which is displaced by the grout can escape out of the open first end 14 and along the channels 24. Similarly the grout applied to a rock bolt 10 will initially fill the internal space 18 before flowing out the open end 14 and passing back externally to the rock bolt 10 to the second end 16 along the channel means. Accordingly, the appearance of grout exiting the channel means at the second end 16 provides the operator with an effective indicator of a maximum amount of grout to be used in any particular rock bolt 10 installation.

Following installation of the rock bolt 10 into a bore hole, an insertion member 70 may be inserted into the rock bolt 10 second end 16. In such cases the expansion means are aligned with the rock bolt 10 second end 16 and forced by known means, such as with a jumbo, into the internal space 18. As the expansion means penetrates into the internal space 18 it engages with the inwardly disposed channel 24 displacing them outwardly as shown schematically in FIG. 8. The displacement of the channel 24 urges the rock bolt 10 lobes 22 into an outward expansion for effecting a tighter communication between the rock bolt 10 and the bore hole.

Once the outward expansion and contact between the lobes 22 and a bore hole surface is maximised any additional displacement caused by the expansion means may be accommodated by a distortion of the channel means. Preferably the distortion has a plastic and elastic component, such that upon removal of the expansion means a channel 24 can substantially restore to its original shape and position whereas the lobes 22 contact surface 41 remains in a flattened out configuration substantially complementary to and in engagement which the bore hole surface.

It is to be understood that an installed rock bolt 10 with expansion means fitted may also be grouted by known means. A grout may be applied to the rock bolt 10 second end 16 and pass through the portion internal space 18 which is unobstructed by the expansion member 70. As with the above description the displaced air can escape via the open first end 14 and between a bore hole surface and the external channel means to the rock face. Similarly, the grout may also flow out the first end 14 and back to the rock face externally, to the rock bolt 10 along the channel means.

It is to be understood that the above description need not be carried out in the order described or with in any particular time frame. For example a rock bolt 10 may be installed into a rock face without any further expansion. In the event of a known or suspected rock face movement or possible bore hole expansion an operator may fit one or more insertion members 70 to an installed rock bolt 10 in order to tighten or re-fix the rock bolt 10 within the bore hole. Similary mesh plates comprising an elongate portion may be removed and replaced as required.

Alternatively a rock bolt 10 installed and grouted in accordance with the above description may subsequently have an insertion member 70 fitted therein.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. 

1. A rock bolt for use in stabilising a rock body, the rock bolt comprising a body having a first open end, a second open end and a length along a longitudinal axis, the body comprising a wall having an internal surface defining an internal space, wherein the wall comprises a plurality of elongate lobes spaced apart and connected together by channel means running, at least in part, along the length of the rock bolt.
 2. A rock bolt according to claim 1, wherein the channel means comprise wall sections connected together and configured to provide a substantially resilient inwardly disposed junction between adjacent lobes.
 3. A rock boll according to claim 1, wherein the rock bolt further comprises expansion means to be received into the internal space for urging the lobes into an outward expansion.
 4. A rock bolt according to claim 2, wherein the expansion means engages with a plurality of inwardly disposed junctions.
 5. A rock bolt according to claim 1, wherein the lobes are evenly spaced around the wall.
 6. A rock bolt according to claim 1, wherein the rock bolt comprises three lobes.
 7. A rock bolt according to claim 1, wherein the rock bolt comprises connection means for assisting in operation and handling of the rock bolt.
 8. A rock bolt according to claim 1, wherein the connection means comprises a collar disposed proximal the second end, the collar and the rock bolt joined together by a tall circumferential join.
 9. A rock bolt according to claim 7, wherein the rock bolt comprises a portion substantially free of channel means.
 10. A rock bolt according to claim 9, wherein the portion is disposed between the connection means and the second end.
 11. A rock bolt according to claim 1, wherein each lobe comprises a contact surface for abutting a bore hole surface.
 12. A rock bolt according to claim 11, wherein each contact surface comprises a portion having a greater curvature than the bore hole before insertion of the expansion means.
 13. A rock bolt according to claim 3, wherein the expansion means comprises an insertion member.
 14. A rock bolt according to claim 13, wherein the insertion member comprises a solid bar ha mg a cylindrical configuration.
 15. A rock bolt according to claim 13, wherein the insertion member comprises a hollow tube having a cylindrical configuration.
 16. A rock bolt according to claim 13, wherein the insertion member comprises a wedge piece.
 17. A rock bolt according to claim 16, wherein the contact surface is configured to be deformable upon insertion of the expansion means so as to improve a contact with the bore hole surface.
 18. A rock bolt according to claim 17, wherein the deformation has a plastic component, such that upon removal of the expansion means the contact surface remains in substantial contact with the bore hole surface.
 19. A rock bolt according to claim 1, wherein the rock bolt is configured to receive and restrain a mesh plate having a suitably sized elongate portion inserted into the internal space.
 20. A rock bolt according to claim 19, wherein the plurality of junctions engage and restrain the expansion means and/or the elongate portion. 